Conventionally, sewing machines allowing detachable attachment of an embroidery unit, housing an embroidery frame carrier mechanism therein, to a sewing machine bed (free arm) have been provided, which embroidery unit allows embroidery sewing operation by moving an embroidery frame holding a workpiece cloth in two perpendicular directions (X, Y directions). In such types of sewing machines, various types of utility stitches such as lock stitches and zigzag stitches can be sewn (normal mode) based on cloth feed operation executed by vertically (and longitudinally) moving a feed dog when the embroidery unit is detached (removed).
When the embroidery unit is attached to the free arm, electrical connection is established by connecting the sewing machine connector and the embroidery unit connector. Also, embroidery sewing is executed in an embroidery mode with the feed dog is maintained in a lowered state where the feed dog lowered below a needle plate. In the embroidery mode, the feed dog is prevented from interfering with embroidery sewing by restraining the feed dog from projecting above the upper surface of the needle plate.
For example, JP 3292467 B discloses a sewing machine provided with a mechanism that automatically switches the feed dog from the normal mode to the embroidery mode when the embroidery unit is attached to the sewing machine. In the disclosed sewing machine, the feed dog is vertically moved in synchronism with the vertical movement of the needle bar by placing a vertically moving lever in abutment with an eccentric cam provided on the lower shaft with the embroidery unit in a detached state. The eccentric cam, having integrally provided with a concentric cam disallowing the rise of the feed dog, is arranged movably in the shaft direction, whereupon attachment of the embroidery unit, a presser piece rotates a horizontal rotary lever which in turn slides the eccentric cam to bring the vertically moving lever in abutment with a concentric cam, thereby maintaining the feed dog in the lowered state.
Recent demands to sew larger embroidery patterns have increased the size of the embroidery frames, and consequently the size of the embroidery unit. Under such circumstances, sewing machines have been suggested that allows the embroidery unit to be used as an auxiliary table and allow execution of cloth feed by the feed dog with the embroidery unit attached to the free arm (embroidery frame removed). In such case, since both utility sewing and embroidery sewing can be executed with the embroidery unit attached, the user must be allowed to switch the mode of the feed dog between the normal mode and the embroidery mode.